For myself, I remain without a strong opinion. On the one hand, I think an octave is a good, solid, traditional practice that could put Pentecost (rightly) up there with Easter and Christmas. On the other hand, Pentecost is preceded by a novena, the original and primal novena even, and maybe this holds that function and should be privileged as such.
In any case, somewhat à propos of the question, there's an interesting note in my Italian ordo:
In the places where, according to custom, the faithful participate in the Mass on the Monday and Tuesday after Pentecost, the readings of Pentecost Sunday are used again, or those proposed in the Rite of Confirmation are proclaimed.(Without prejudice, of course, to the Monday now being the obligatory memorial (with the power to displace any other obligatory memorial) of the Blessed Virgin Mary, Mother of the Church.)
Personally, I don't have any experience of the Pentecost Monday and Tuesday that the Italian ordo mentions. Maybe folks who do can share about them in a comment.